Method and apparatus for casting pipes centrifugally



y EMM@ March s, 1934.

N. F. S. RUSSELL ET Al.'

METHOD AND APPARATUS FOR CASTING PIPES CENTRIFUGALLY Filed oct. 19. 19523 sheets-snm 1 s W w la Y v HM M 5.4 r

March 6, 1934. N. F. s. RssELL ET Al. 1,949,433

METHOD AND APPARATUS FOR. CASTING PIPES CENTRIFUGALLY Filed oct 19, 1952Jamas-sheet 2 //V VE A 70195 Arran/5y.

Marci@ 34 N. F. s. RUSSELL Er A1. 1,949,433

METHOD AND APPARATUS FOR CASTING PIPES CENTRIFUGALLY Filed Oct. 19, 19523 Sheets-Sheet 3 /Gi /G Ffm L Patented Mar. f6, 1934 UNITED STATESMETHOD AND APPARATUS Foa CASTING Piras CENTRIFUGALLY Norman F. S.Russell and Frederick C. Langenberg, Edgewater Park, N. J., assignors toUnited States Pipe and Foundry Company, Burlington, N. J., a corporationof New Jersey Application October 19, 1932, Serial No. 638,480

' 11r claims. (c1. zz-zo'o) Our invention relates to that method ofcasting pipes in which the molten metal is progressively delivered to arotating mold through a relatively retractable runner so that the metalis delivered to the mold in helical coils with over-lapping edges whichfuse together to form a continuous casting and, more especially, ourinvention is adapted for use with externally cooled metal molds althoughit can be usefully applied in 13 connection with other kinds of pipemolds. The object of our invention is to provide a practical and eicientmethod and apparatus 'whereby a thin coating of a powdered coatingmaterial can be progressively applied to the inner surface of the moldin over-lapping helical coils in immediate advance of the contact of themolten metal with the mold and-in such manner as to build up a coatingof the powdered material of substantially uniform thickness andremarkable efliciency in the production of a casting having uniform anddesirable qualit-ies.

We are aware that it has heretofore been proposed to apply a coating tothe inner surface of metal moldsused in casting pipe but, so far as weare aware, no method heretofore proposed, used, or experimented with,has been effective in use to bring about a coating of the mold with aloose, dry, powdered material which will maintain its coherence andcontinuity as a coating during the casting operation and result in theproduction of a casting of uniform and desirable structure. Our studiesand experimentsin developing our invention have developed that thefailure of methods heretofore proposed is due to many causes, amongwhich may be mentioned the difficulty met with in effecting an evendistribution of the coating material over the surface of the mold.Again, we have found that a coating of dry, powdered material is liableto become fractured or displaced in parts so as to leave bare, uncoveredspots of mold surface if the coating is left too long in contact with,the mold surface before it is covered by the molten iron and this `isthe more liable to occur as the thickness of the 4 coating is increased.Again, we have found that f the impact of the metal with the coatedsurface of the mold has a tendency to fracture the-coating, pushingportions of the coating over the mold surface so as to leave unprotectedareas which bring about areas of chill in the casting and also bringabout very undesirable rougheningof the outer surface of the casting andwe have found that this liability to displacement of the coatingmaterial notably increases with increase in the thickness of the coatinglayer.

Broadly speaking, our invention has for its leading feature theprogressive building up of a coatlng of powdered material upon theinside ofthe mold and in immediate advance of the Contact of the moltenmetal with the coated surface of the mold by means of a jet of carriergas carrying distributed particles of a powdered coating material andprogressively directed toward those portions of the mold which are to beshortly thereafter contacted by the molten metal. The energy of the jetof carrier gas should be such as to iinpart sufficient velocity to theparticles-of coating material to carry them into contact with thevsurface of the mold without the jet of 4gas itself having such velocityas to impinge on the mold surface with any substantial velocity and thepcwdered coating vmaterial should be fed to the gas jet at a uniformrate of speed so as to result in the production of a coating layer of asubstantially uniform thickness and we have vfound that a coatingproduced in this Way has certain'distinguishing and valuable qualitiesin that the coating has good resistance to disruptive forces, can be,applied to the mold with great uniformity even when the coating is verythin and has, even when 30 the coating is very thin indeed, an effect inpreventing the formation of chilled areas in the casting which wouldseem to be explainable only on the assumption that the particles 'ofcoating material impelled by the carrier gas against the mold aresurrounded by an adsorbed lm of the gas, which films, for an appreciabletime after the coating is deposited, form an effective part of thecoating and perform an important function in bringing about the absenceof chill and a desirable structure in the casting.

Another important feature of our invention has to do with the iniervalof time which may be per'- mitted to elapse between the time when thecoating is applied to the mold and the time when the so applied coatingis contacted by the molten metal issuing from the spout of the runnerand as to this the maximum time during which the coating should bepermitted to remain uncovered by the melted metal should not exceed sixseconds and, for the best results, should be as short as possible. Bypreference, we direct the jet of carrier gas so that it'will deposit itsparticles of coating material upon that4 portion of the mold which, atthe time of deposit, lies immediately m5.

above and close to that portion of the mold upon which the molten metalis being poured so that the coating is contacted by the molten metalalmost instantly. It must be understood that the jet of carrier gas mustbe so directed as to deposit its particles of coating material upon theuncovered mold surface without bringing any appreciable amount of thecoating material into direct Contact with the metal issuing from thespout oi the runner or with the molten metal which has already beendeposited in the mold and that, with clue observance of this condition,the closer the coating is applied to the metal issuing from the runnerand to the previously poured coil of metal, the better, and we stronglyrecommend that the gas jet should be directed with these conditions inview, against the upper surface of the mold. Reasons which influence usin directing and recommending the progressive direction .of the gas jetagainst those portions of the Amold which are to be contacted by themetal issuing from the runner in a very brief interval of time, are,that we have found that the longer the coat ing remains on the surfaceof the mold before it is contacted by the metal, the more liabilitythere is for portions of the coating material to slip or becomedisplaced,l leaving uncovered areas, the existence of which brings aboutundesirable qualities in the casting and, besides this, our experiencewith the process has convinced us that the longer the intervalintervening between the laying of the coating and its contact with themelted metal, the less efficient is the coating even when its continuityis not impaired and this we believe to be explainable only on theassumption that the adsorbed films of gas adhering to the particles ofcoating material when they are deposited upon the surface of the moldform an important but short-lived element of the coating layer.

Another and important feature of our invention has to do with thethickness of the coating layer which will bring about the best results.This is determined by the amount of coating material fed to anddelivered by the carrier gas jet during the casting of the pipe and asthere is a draft of air through the mold during the casting operationwhich undoubtedly carries away a part of the powdered coating materialdelivered to the mold by the gas jet, it i's impossible to statedefinitely what the actual thickness of the coating effected by anyspeciflc rate of feed is. We have found, however, that with all thecoating materials'with which we have worked or experimented it isdistinctly detrimental to the efiiciency of the coating produced to feedto the mold, during the casting process, -powdered coating material ingreater quantity than would, if it all remained in contact with themold, form a coating of a thickness exceeding .001 of an inch and wehave found that in all cases the powdered coating material should not befed to the mold in greater quantity than that minimum quantity less thanthe amount which would producey a coating of .001 of, an inch inthickness which will result in the production of a casting without areasof chill. This will vary somewhat with different powdered coatingmaterials but can be readily ascertained and, when once ascertained, canbe applied with uniformity and assurance as to good results. Workingwith powdered ferro-silicon which will pass a sieve of thirty meshesto-the inch, we have found that the feed of ferro-silicon to the gas ietshould, `for the best results, be in such amount as would produce, ifall the coating material re maimed in position in the mold, a-coating ofap@ proximately ,0003 of an inch in thickness.

Working with other coating materials we have found that the feed willvary. Thus, with kaolin, we have found that the feed should be at a ratewhich would produce a coating, if it all remained in contact with themold, of ,0009 of an. inch; with talc, the feed should be at the rate of.0009 of an inch; with magnetite, the feed should be at the rate of.0005 of an inch; with ferro-manganese, the'feed should be at the rateof .0007 of an inch; with zirconium manganese silicon, the feed shouldbe at the rate of .0003 of an inch; with mica, the feed shouldibe at therate of .0008 of an inch; and with seacoal, the feed should be at therate of .001 of an inch. It will be understood from what we have saidabove that coating materials such as ferro silicon, which will form aneficient coating of minimum thickness, are deinch are distinctlyinferior for use in our process.

Aside from the fact that the thicker the coating deposited upon the moldthe more liable it is to fracture and loss in continuity, it would seemclear from our work with this process that the thinner coatings resultin the production of castings vof the most desirable structure.

In the casting of bell ended pipe in which the mold is formed with abell into which is inserted a core, it is not, of course, practicable tolay down upon the bell portion of the mold such a uniform coating ascan, by our process, be applied to the cylindrical portion of the mold.In view of the fact that the casting is heavier in the bell portion,

it is not so important that the bell should be coated as it is withregard to the cylindrical portion of the mold but by directing the gasjet with distributed particles of coating material into the portion ofthe bell which lies between the end of the core and the beginning of.the cylindrical portion of the mold for a short interval before thepouring of the metal begins, we have found it practicable to bring aboutatleast a. reasonably satisfactory coating of the bell portion of themold.

Our invention further relates to the provision of a suitable andefficient apparatus for carrying into effect the improved process whichwe havey conveyance of a carrier gas and having at its end adjacenttothe free end of the runner, a nozzle adapted to deliver a jet of thecarrier gas, of suitable form and dimensions, toward such portions ofthe inner surface of the mold as should, at the time, have a coatingapplied to them. This involves that the gas nozzle should occupy a iixedposition with reference to the delivery spout of' the runner and, forthe best results, the nozzle should be so located and directed that thejet issuing from it should be directed at that portion 4, Y of the moldwhich lies immediately above the.'

portion upon which, at the time, metal is being delivered from the spoutof the runner and, again,

the relative locations of the spout of the runner and of the carrier gasnozzle should be such that when the runner is fully inserted in the moldso that the runner spout registers with the end of the bell, atleast aportion of the iet issuing from. the gas nozzle should also registerwith the end of the provision, at the end of the gas conduit'opposite tothat to which the nozzle is applied, of means for injecting a jet of thecarrier gas into the conduit and of feeding into this jet a. regulatedquantity of the powdered coating material.

The above' and other features of our improved apparatus will be bestunderstood as described in connection with the drawings which illustratea pipe casting machine provided with our improvements in what we believeto be their best form and in which v Figure 1 is a side elevation of apipe casting machine provided with our improvements, with the mold andsurrounding water chamber shown in vertical longitudinal section andwith the supporting frame and tracks upon which the mold carriage moves,broken away at the left hand end of the view and somewhatdiagrammatically indicated, as is also the case With the details of oon-I `,struction of those parts of the apparatus which in themselves formno part of our invention and are of well known and familiarconstruction.

Figure 2 is a plan View of the delivery end of the runner through whichmolten metal is delivered to the mold, showing the carrier gas conduitand nozzle` which are supported upon the runner. One side of the mold isshown in section and the position of impact with the mold of the metalissuing from the spout of the ruimer with reference to the edge of the'previously deposited helical coil of metal, is also roughly indicated.It will be understood that the position of the runner and partssupported thereon, with referencev to the mold, is, as shown in thisfigure, somewhat yretracted from the position shown in Fig. 1.

Figure 3 is a side elevation of the parts of the runner and carrier gasconduit with their spout and nozzle as shown in Fig. 2.

Figure 4 is an elevation of the delivery nozzle and the carrier gasconduit shown, for the most part, on the section line 4-4 of Fig. 2, andshowing the union of the nozzle with the conduit pipe. Figure 5 is across sectional view on the line 5-5 of Fig. 2, with the surroundingportion of thel mold also shown in section and the areas of contact withthe mold of the metal issuing from the spout of the runner an-d the dustissuing from the nozzle of the gas conduitalso indicated.

Figure 6 is a perspective view showing that portion of the mold uponwhich the molten' metal land the coating of pulverized material arebeing simultaneously deposited.

' Figure '7 is a plan view of the end of the runner and the partssupported thereon, shown'in connection, with one side of the mold shownin horizontal, central section and provided with the core which isinserted in the bell end of the mold. This is a scale drawing of theillustrated parts in the proportions in which they exist in an apparatusadapted for the casting of a six inch pipe, involving the use of a moldhaving the proportion of acylindrical portion of 7 inches internaldiameter, the parts being shown in the relative positions they occupy atthe beginning of the casting operation.

Fig. 8 is a Vertical section taken on the line 8-8 of Fig. l, showingthe mechanism provided for feeding the pulverized coating material tothe carrier gas conduit.

Figure 9 is a cross sectional view o f the container for the powderedcoating material and connected devices, taken on the section line 9 9 ofFig. 8, with the mechanism for adjusting the feed of powdered materialshown in plan.

Figure 10 is a sectional elevaticn'of the rear portion of the carriergasA conduit and of the hopper through which the powdered coatingmaterial is fed to the conduit. A

Figure 1l is a plan view of the delivery end of the runner for moltenmetal, showing a modification in the dispositionl of the carrier gasnozzle, and Figure 12 is a View similar to Fig. 11, with the jointsbetween the air conduit and between the off-set portion and the gasnozzle shown in section. A

A indicates the frame supporting the casting machine and its appliances.B indicates a supporting structure erected on the frame to support theladle B1, from which metal is fed to the rimner. B2 'indicates ahydraulic cylinder coupled to actuate the ladle. C indicates the runnerwhiohis secured to the structure B and is of usual construction,provided at its end with a spout C1 inclined to one side. The runner, aswe have said, is of usual construction except that it has formed alongthe side toward which the spout C1 extends, a recessed seat C2' adaptedto receive the carrier gas conduit. D indicates the water box carriagethrough which extends the rotatable mold D1, d1 indicating the annularring provided at the spigot end of the mold and projecting inwardly tothe depth of the projected Wall thickness of the casting. The carriage,as is usual, is supported on wheels vindicated at D2, resting upon thetracks A1 on the top of the framing A. The framing and tracks are partlycut away in Fig. 1, but it will be understood that the construction is,as usual, such as to permit the longitudinal travel of the moldvcarriage with respect to the stationary runner. D3 indicates a motorsupported on the mold carriage and connected as by gearing indicated atd3 to drive the mold D1. Longitudinal motion is given to the moldcarriage by the hydraulic cylinder D4. The piston, not shown, working inthe cylinder is coupled through its piston rod D5 to the mold carriage.D6 indicates the bell end of the mold and D7, Fig. '7, indicates thecore which is inserted in the bell end' of the mold before metal ispoured into it, D8, Fig. 7, indicating the space intervening betweenythe end of the core and the beginning of the cylindrical portion of themold.

In all of the above features of general construction, the apparatus isof the familiar type of construction used in the method of progressivelycasting pipe in a centrifugal mold which, during' the casting operation,is retracted relatively to the stationary runner through which the metalis flowing into the mold.

E indicates a' conduit for acarrier gas, such as air, which, as shown,is supported on the runner C, preferably as shown, in the recessedportion C2. To the end of this -gas conduit, which lies near the end ofthe runner, is secured a nozzle E1 which is directed in such manner thatit will deliver the carrier gas fed to it by the gas conduit outwardlytoward the side of the mold toward which the runner spout C1 alsoextends. The essential constructive features of this nozzle are that itwill deliver the carrier gas and the powdered coating material which itconveys, in ,a direction which will deposit the coating material on theside of the mold in advance of the contactV of'the metal issuing fromthe spoutof the runner with the so coated portion of the mold and alsodeliver the powdered coating material upon the surface of the mold at apoint at a distance, so to speak, in front of the freshly laid coil ofstill uid metal, these conditions being necessary to terial with thefluid metal already/.deposited in the mold and that issuing from thespout of the runner. For the best results, the carrier gas nozzle shouldbe so located and directed as to deliver the coating material upon thesurface of the mold in immediate advance ofthe contact lof the meltedmetal'issuing from the runner so that the deposited coating will becontacted by the metal issuing from the spout of the runner almostimmediately after its deposition o-n the mold. While we haveexperimented with varying degrees of success with many forms of nozzles,we have found the nozzle construction indicated in the drawings to beespecially well adapted forv our purposes. This nozzle, as shown, is ofgradually contracting cross sectional area from its union with the gasconduit, preferably conical as shown at E2, and is provided with threeparallel rows of holes, as indicated at E3, E4, E5, the aggregate areaof the holes being about three times the cross sectional area of the gasconduit. This special construction of the nozzle was not invented by usbut is shown simply as the one' which We have vfound best adapted forthe practice of our invention. It is desirable that the nozzle should beso located as to lie quite close to that portion of the mold to which itis directed. The actual distance which will exist between the nozzle andthe mold when the runner to which the nozzle is attached is inserted inthe mold is determined, to a certain extent, by the radial thickness, soto speak, of the ring d1 at the spigot end of the mold because thenozzle must be so placed as to pass this ring without contacting with itwhen the runner is withdrawn from the mold. In molds of the largerdiameters We connect the carrier gas conduit to the nozzle by means ofan off-set section indicated in Figs. 11 and 12, at E6, this offsetportion being so curved, as indicated, as to bring the nozzle to thedesired proximity to the side of the mold. 'I'he other end of thecarrier gas conduit is connected with what we may call the gun, theunion being indicated at E". This gun is formed with a cylindricalpassage Fl of the same diameter as that of the gas conduit with which itcommunicates and at its outer end a nozzle F2 enters the end of thispassage, this nozzle being, as shown, connected with an air hose whichin turn is connected with any source, not shown, of compressed air orother available gas. Opening into the cylindrical passage F1 is apassage F5, leading from a funnel F4 which is erected to receive ameasured feed of pulverized coating material from any suitable feedingapparatus. We have indicated the air conduit leading to the nozzle F2 atF5, F6 indicating a pressure gauge connected with this air conduit andF7 a regulating valve.

It is very important for the most successful application of ourinvention that the powdered coating material should be fed to the gunand through the carrier gas conduit to the delivery nozzle with greatregularity so as to effect the coating of the mold with a uniform depthof coating material and for this purpose we have found the feedingapparatus indicated in the drawings to be especially well adapted thoughit is not in itself our own invention. This feeding apparatus consistsof an upright cylinder G in the lower portion of which is secured arotatable disc Gl, the upper surface of which should bev-grooved orotherwise roughened, as indicated at G2, so as to take a better holdupon the powdered coating material which is charged into the cylinderand rests upon this disc. a1 indicates packing employed to make areasonably close joint between the disc and the cylinder. The disc issupported on a rotating spindle G5 which by any convenient gearing, notshown, is driven by a motor, as indicated at G4, and from the uppersurface of the disc projects a spindle G5 from which extend at differentlevels lateral arms G5 connected by vertical rods G", the framing thusformed being intended to facilitate the rotation of the charge ofpowdered coating material with the disc. Through 'the wall of thecylinder G is formed a slot-like opening G located, as shown, just abovethe disc. To one side edge of this opening G5 is hinged, as indicated atH1, a knife blade H which extends across the opening with its sharp edgeH2 projecting into the cylinder through the-opening G8 and `to the topof this knife blade is secured a flanged extension H3 which is providedto prevent the escape of the powdered coating material over the upperedge of the knife. From the hinged side of the knife extends a shaft H4,to the upper end of which is secured a lever H5 having a forked end H6in which is journalled a worm I which is turned by means of a button I1and secured in any desired position by means of a clamping screw I2.This worm is in engagement with a sector I3 and it will readily be seenthat by turning the worm any desired adjustmentof the knife blade can beeffected. J indicates a cover for the hopper F4. This cover is providedto protect the hopper from the intrusions of undesirable material but itis provided with openings to permit the inflow of air. A similar coverJ1 is indicated for the cylinder G.

K, Figs. 2 and 5, indicates the stream of molten metal -issuing fromth'e runner spout C1 and the area of impact of this stream of moltenmetal with the side of the mold is indicated at K1 in Figs. 2, 5, and 6.K2, Fig. 6, indicates the last previously poured coil of metal and K3,Fig. 2, indicates in section the cast metal in contact with the wall ofthe mold. L, Figs. 2 and 5, indicate the lines on which the dust issuingfrom the nozzle travels on its way to contact with the side of the mold.Llvindicates the location on the side of the mold of the pad of dustdirectly applied to it by the nozzle.

It will be understood that the parts of our apparatus are shown in Figs.1 and 7, in the relative positions they occupy at the beginning of thepouring of molten metal to form a bell ended cast iron pipe. After themolten metal is fed from the, ladle into the runner and begins to issueinto the mold from the nozzle of the runner the parts remain relativelystationary, except that the mold is in full revolution, until sufficientmetal has owed into the mold to fill the space between the bell and thecore. Where it is desired to at least partially coat the bell end of themold with the powdered coating material, we j turn on the jet of carriergas with its load of powdered coating material so that the powder willbe delivered into the open end of the bell slightly in advance of theflow of metal from the spout of the runner. This is made practicable byhaving at least a portion of the carrier gas jet so located as todeliver the powder into the open end of the bell at the same time'v thatthe nozzle of the ruimer registers with the open end of the bell. Afterthe bell end of the casting is poured, the mold is retracted with theresult that the metal issuing from the nozzle o f the runner isdeposited on the cylindrical portion of the rotating mold in helicalcoils which. fuse together at their contacting edges to form acontinuous lar portion F1 of the ,gun F and at the same time the feedingapparatus delivers a nicely regulated feed of powdered coating materialinto the .funnel F4 and through it into the tubular portion of the gunso that it is carried through the carrier gas conduit with the air and`into the nozzle El Vfrom which it issues together with the carrier gasand by the kinetic energy imparted tothe particles of coating materialin its passage through' the conduit E, these particles are impelled intocontact with the side of the mold where they form a layer or coating,the depth of which depends, of course, upon the quantity of powderedmaterial fed to the carrier gas and the percentage of this powderedmaterial which actually remains in contact with the sidesof` the mold.This coating layer will be deposited upon the mold in helical coils asis the case with the metal issuing from the runner and the breadth ofthe coils and the pitch of the helix will be such that the coils ofcoating material will somewhatoverlap, thus insuring that ,the entiresurface of the mold is coated. The location of the dust nozzle E1 withreference to the metal delivery nozzle C1 must be lsuch that it willdirect the powdered coating material issuing from it toward that portionof the mold which is not contacted at the time that powder is depositedby the stream of metal issuing from the runner or by the previouslypoured helical coil of molten metal and with this requirement in View,the closer the point of application of the coating material tothe moldto the point of impact upon the mold of the moltenmetal issuing from therunner, the better. We have indicated in the drawings the point ofdeposit of the coating material as in the upper quadrant ofthe moldimmediately above that lower quadrant upon which the metal from therunner is deposited so that the coated surface of the mold is contactedby the metal issuing from the spout of the runner by the rotativemovement of the mold through less than 90 or, in view of the speed withwhich the mold is rotated, almost instantly after its deposit upon themold and it will be seen that the application of the pad of coatingmaterial at the point indicated is greatly facilitated by theconstruction shown in the drawings in which the carrier gas conduit andnozzle are supported on that upper side of the runner which lies to thesame side of the runner as that from which the spout Cl extends. It willalso be seen that by providing the rlmner with a recessed seat. such asindicatedlat C. and locating the carrier gas conduit in this recessedportion of the runner, this part of the apparatusis greatlyl compacted,which is desirable in all constructions and important in theconstruction of apparatus for the manufacture of small diameter pipes.

While, obviously, our invention can be availed of in modied forms of theapparatus shown and described, we. would point out that the location ofthe gas nozzle on the upper side'of the.

runner and its direction toward the upper side of the mold, are highlypreferable features, both from the point of view of compactness in thestructure `of the apparatus and because this l0- cation of the nozzleenables the carrier gas and the dustto be most conveniently directed soas to deposit the coating on the upper side of the mold and as close aspracticable to the point of contact of the metal issuing from the spoutof the runner.

Having now described our invention. what we claim as new and desire tosecure by Letters Patent, is:

1. In the casting of pipes frommolten metal in externally cooledcentrifugal metal molds having a cylindrical section, the method stepswhich consist in building up upon the cylindrical portion of the mold-acoating of iinely divided dry coating material by progressivelydirecting a jet of carrier gas charged with finely divided dry coatingmaterial against successive portions of the surface of the mold to be socoated and then centrifugally casting molten metal in the so coated moldto form a pipe.

2. In the casting of pipes from molten metal in externally cooledcentrifugal metal molds having a cylindrical section, the method stepswhich consist in setting the mold in rotation, then building up upon thecylindrical portion of the rotating mold a coating of finely divided drycoating material by directing against said cylindrical portion of therotating mold a jet of carrier gas charged with particles of finelydivided dry coating material and then pouring molten metal into the socoated cylindrical portion of the rotating mold to form thevcylindricalportion of the pipe. 3. In the method of casting pipes in which themolten metal is progressively delivered to an externally cooled rotatingmetal mold having a cylindrical section through a relatively retractingrunner in such manner that the metal is delivered to the cylindricalportieriy of the surl face of the rotating mold in the form of a helix,

the method steps which consist in setting the mold in rotation prior tothe delivery of molten metal thereto, progressively building up upon thecylindrical surface of the rotating mold a coating of nely divided drycoating material made up of a helical band, so applied to the surface ofthe mold that adjacent coils of the helix will overlap, by directingfirst against the end of the cylindrical portion of the mold a jetA of acarrier gas charged with finely divided dry coating material and thenprogressively relatively retracting said charged jet throughout thelength .of the cylindrical portion of the rotating mold at a rate ofspeed substantially equal to that at which the runner delivering moltenmeta-l to the mold is relatively retracted and during the progressiveapplication of the coating to the rotating mold progressively feedingmolten metal to the cylindrical portion of the mold through therelatively retracting runner in such manner that the progressivelycoated portions of the mold are contacted by molten metal shortly afterthe deposit of the coating thereupon.v

4. In the method of claim 3, the further step which consists in socoordinating the progressive deposit of the coating upon the mold and.the progressive deposit of molten metal upon the coated surface thatfreshly coated areas of the rotating mold surface will be contacted bythe molten metal within six seconds of the time that the coating isapplied thereto.

5. In the method of claim 3, the further step which consists in socoordinating the progressive deposit of the coating upon the mold andthe progressive4 deposit of molten metal uponV the coated surface thatfreshly coated areas of the rotating mold surface will be contacted bythe molten metal within the period of time in which the rotating mold ismaking one complete revoiution.

6. In the method of claim 3, the further step which consists in socoordinating the progressive deposit of the coating upon the mold andthe progressive deposit of molten metal upon the coated surface thatthe, coating will be applied to areas of the rotating mold surface lyingabove the point of impact of the molten metal upon the surface of themold and to be contacted by the molten metal before the mold hascompleted one revolution.

7. In the method of claim 3, the further step which consistsv in soregulating the charge of dry iinely divided coating material with whichthe carrier gas jet is charged that the total amount of coating materialprogressively delivered by the carrier gas jet to the inside of thecylindrical portion of the mold will not exceed ,a quantity which, 'ifevenly and compactly distributed over the cylindrical portion of themold, would form a coating of .001 in thickness.

8. In the method of claim 3, the further steps which consist in socoordinating the progressive ,the quantity of finely divided dry coatingmaterial delivered by the jet of carrier gas that the total quantity ofsuch iinely divided dry coating material delivered by the `iet duringthe progressive formation of the coating shall not exceed that quantitywhich, if evenly and compactly distributed over the cylindrical portionof the mold, would form a coatingof .001" in thickness.

9. In the method of claim 3, the further steps which consist in socoordinating the progressive deposit of the coating upon the mold andthe progressive deposit of molten metal upon the coated surface thatfreshly coated areas of the rotating mold surface will be contacted bythe molten metal within the period of time in which the rotating mold ismaking one complete revolution and in so regulating the quantity offinelyv divided dry coating material delivered by the jet of carrier gasthat the total quantity of such nely divided dry coating materialdelivered 10. In the casting of pipes from molten metalin externallycooled centrifugal metal molds having a cylindrical section, the methodsteps which consist in setting the mold in rotation, then, prior to thedelivery of molten metal to coated portions of the rotating mold,building up upon the cylindrical portion of the rotating mold a coatingof finely divided dry coating material permeated with adsorbed films ofthe carrier gas by directing against said cylindrical portion of therotating mold a jet of carrier gas charged with particles of finelydivided dry coating material and pouring molten metal into the so coatedcylindrical portion-of the rotating mold before a material portion ofthe entrained gas lms are eliminated from the composition of the coatingand within a period of six seconds after the deposit of the coating uponthe surface of the mold to form the cylindrical portion of the pipe.

11. In a pipe casting machine comprising a rotatable mold and arelatively reciprocable runner adapted to deliver molten metalprogressively to the rotating mold, the combination therewith of aconduit for a carrier'gas secured to and supported by the runner so asto be relatively longitudinally movable with respect to the mold to thesame extent as is the runner, a delivery nozzle for a carrier gascharged with'flnely divided dry coating material supported by andmovable'with 'the runner and so located with respect to the delivery endof the runner and the inner surface of the mold as to direct a jet ofthe carrier gas progressively towards those portions of the mold whichby the rotating movement of the mold and the simultaneous relativeretraction of the runner are, shortly after the application of thecoating material, contacted by the molten metal issuing from the runner,a carrier gas conduit connectedl to the nozzle, means for delivering ajet of carrier gas to the outer end of the gas conduit and means forfeeding a pulverized mold coating material into the'carrier gas conduit.

NORMAN F. S. RUSSELL. FREDERICK C. LANGENBERG.

